In connection with a conventional printed circuit board, having a capacitor buried in a substrate thereof, reference is had to, for example, the following publications:
(1) Publication of JP Patent No. 2738590, and
(2) Publication of JP Patent Kokai JP-P2001-320171A.
Of these, the publication (1) (Publication of JP Patent No. 2738590) discloses a capacitive printed circuit board including a capacitor laminate and a plural number of devices respectively connected to different portions of the capacitor laminate, in which the capacitor laminate is made up by laminated dielectric sheets and two electrically conductive foils, arranged on both sides of the laminated dielectric sheets, and having a first surface surface-processed to present a surface roughness sufficient to exhibit adhesion to the laminated dielectric sheets, in which the second surface of each electrically conductive foil opposite to the first surface is surface-processed to present a surface roughness to exhibit adhesion within the capacitive printed circuit board, in which the capacitor laminate is made up by one dielectric sheet and two electrically conductive foils, as the first surface of said electrically conductive foil is tightly contacted with the dielectric sheet and in which the dielectric sheet is of the minimum thickness in all portions thereof facing the electrically conductive foil. Specifically, the above Publication 1 discloses a structure of a capacitor laminate in which electrically conductive layers are arranged on both sides of an organic dielectric layer to operate as a capacitor. However, with this structure, the capacitance cannot exceed the limit of approximately several nF at most.
In a well-known manner, there are three techniques for increasing the capacitance C of a capacitor, that is                increasing the surface area of an electrode;        reducing the separation between the electrodes (or reducing the thickness of the dielectric layer between the electrodes); and        increasing the dielectric constant of the dielectric layer.        
However, in light of product reliability, such as electrical insulating properties, or manufacture process, it is difficult to reduce the film thickness of the dielectric layer to 1 μm or less. It is similarly difficult to increase the dielectric constant of the dielectric layer drastically.
For increasing the surface area of the electrically conductive layer of the facing capacitive electrodes, the metal surface is roughed to apparently increase the surface area, as described in Publication 1. However, with the technique described in Publication 1, the surface area of the facing electrode surfaces cannot be actually increased, and hence a sufficient performance cannot be achieved.
There is also a method of burying a component, operating as a capacitor, in the bulk of the printed circuit board. However, the buried type capacitive component prescribes the substrate thickness or the electrode contact site and thus imposes constraint on the degree of freedom in substrate designing.
The second Publication (Publication of JP Patent Kokai JP-P2001-320171A) discloses a structure comprising a dielectric layer for a capacitor, formed of aluminum oxide, which covers the surface of the aluminum substrate, and a plating layer for a capacitor electrode, which is formed to cover the surface of the dielectric layer for the capacitor. The aluminum substrate, the dielectric layer for the capacitor and the plating layer for the capacitor electrode go to make up a capacitor in a multi-layered circuit substrate to eliminate the necessity of embedding a chip capacitor in an inter-layer insulating film to reduce the thickness of the inter-layer insulating film thereby reducing the thickness of the multi-layered circuit substrate in its entirety. This Publication (2) indicates that a dielectric film for a capacitor of Al2O3 may be formed by oxidizing the surface of the aluminum substrate with oxygen plasma to form a dielectric film for the capacitor of Al2O3 as a surface layer or to deposit powders of Al2O3 on the surface of an aluminum substrate formed by sintering. However, the aluminum oxide film, formed by, for example, sintering of the powders, is not up to the requirement for a reduced thickness.